0.—GEOLOGY. 61 
advocated by Ami Boué in 1822 and in 1829 in his ‘ Geognostisches 
Gemilde von Deutschland’ (p. 143), and supported by the general 
association of mineral veins and igneous rocks; he held that extensive 
ore-deposits are found only near ‘ Granite, Syenite, Porphyry and Trap- 
rocks’ (ibid., pp. 42-3). A. L. Necker'® also urged, despite a few 
apparent exceptions, the general ‘ connexion of igneous with metalliferous 
deposits.’ 
In the same year the main alternative explanation—the connexion of 
mineral veins with great fractures—was put forward by J. Fournet in a 
long memoir, ‘ Etudes sur les Dépots Métalliféres,’ published in Amédée 
Burat’s edition of d’Aubuison’s ‘ Traité de Géognosie,’ (vol. III, 1835, 
pp. 383-621). Fournet assigned the minor veins to the filling of shrinkage 
cracks, and small faults; but he regarded the veins of most economic 
value, as deposited along the major faults due to the ‘ violent movements ’ 
that accompany the upheaval of mountain chains. 
That the ores along these fractures were due to rising waters was 
rendered the more probable by the paper contributed by C. G. B. Daubeny?° 
at the 1836 meeting on ‘Mineral and Thermal Waters.’ The deep- 
seated source of the ores was strengthened in the famous memoir by Elie 
de Beaumont on ‘ Les Emanations volcaniques et métalliféres’ in 1847, 
in which he showed the importance of pneumatolyic processes in the 
formation of some ores. Meanwhile, the theory that ores were derived 
from waters percolating through the rocks beside the veins had been 
revived by Bischof (1847), but was generally rejected until his disciples, 
Forchhammer (1855) and especially Sandberger (1882, 1885), found 
particles of the ordinary ore metals in all kinds of ancient rocks. 
The ascensionist views of the deep-seated source of ores was then 
eagerly replaced, owing to the preference for a tangible than for an 
inaccessible source—by the lateral secretion theory, which was extended 
by Emmons and others of the American school. It was dominant for 
twenty years, until in 1893 the deep-seated source of most ores was 
advocated by Posepny in the paper that initiated the present stage of the 
ore genesis investigations. An intermediate view was advocated by J. D. 
Kemp and others who recalled attention to the general association of 
mineral veins with igneous rocks ; and the discovery therein of traces of 
various lode metals led to the view that the constituents of the lodes are 
derived from igneous rocks in which they are as primary components 
as the iron and magnesium in the ferro-magnesian silicates, and the 
mmanganese in the manganese silicates. 
That view is perhaps still the generally accepted theory ; but there are 
serious objections to it: for though there is no inherent improbability in 
the occurrence of small proportions of many metals in the igneous rocks, 
the quantity appears insufficient to have provided the metals of the lodes. 
The frequent association of igneous rocks and ores may be due to both 
having been introduced in consequence of crustal disturbances. Many 
areas with abundant igneous rocks are barren of ores, and such igneous 
rocks as contain the ordinary lode metals show evidence of alteration by 
19 Trans. Geol. Soc. (2) III, 1835, pp. 497-8. 
% 6th Rep. B.A. for 1835, 1837, pp. 1-96. 
